Google's gathering of data from open Wi-Fi access points in the UK as it collected its StreetView data now has a crime reference number: 2318672/10.

That doesn't mean it's definitely a crime, though; that's the investigation number issued on Tuesday by London's Metropolitan Police at the request of the pressure group Privacy International, which alleges that the search company carried out "criminal interception of wireless communications content" and that that constitutes an offence under the Regulation of Investigatory Powers Act and the Wireless Telegraphy Act.

Google has insisted all along that the collection of the data was an accident caused when code left in a production system kept the content being broadcast over the Wi-Fi networks as the Google StreetView car drove past.

Google was mapping the networks' location, names and MAC (Media Access Control) address, which is unique to each network and is broadcast by it and can be picked up by any passer-by equipped with a Wi-Fi receiver. It is not an offence to capture the latter details - but Google also captured content from messages being broadcast over the open networks, which French authorities say includes passwords from emails. Google did not try and would not have been able to access content on password-protected networks.

According to Privacy International, which has been briefed by police on the likely path the investigation will take, the next step will be initial inquiries into the essential facts of the case before deciding which (if any) law may have been breached. The police will need to seek advice on which legislation to focus on, as each involves a different prosecution process. The police estimate that this initial investigation will take eight to ten days, after which the case will be escalated to a specialist team working at the national level. No estimate has been given regarding the likely period of the main investigation.

Google has offered to delete the data relating to the UK. The UK's Information Commissioner acceded to the request, but Privacy International demanded that it be kept so that the police could carry out the investigation.

A number of different countries are investigating whether Google has broken any laws, because it used the same mapping/recording system when it carried out its StreetView sampling in other countries. The company has offered to delete the content data (though not the data about network locations)unread for every country, but only a handful, including Ireland, have agreed.

In some countries local laws have stymied further investigation. In Germany, its equivalent of the information commissioner, an arm of the government, has demanded to see the content - but there are strict rules against government agencies viewing private citizens' data without their permission.

In the UK, the police will need to interview Google staff to find out who the "responsible person" is for this matter.

Simon Davies, PI's Director said "We are pleased that the police have taken up this complaint for investigation. An evidence based approach to this complex matter is sorely needed now. We have already told police that we will cooperate fully with any inquiries. I know Google will want to do the same".

He added: "We hope that this difficult process will give Google pause for thought about how it conducts itself. Perhaps in future the company will rely less on PR spin and more on good governance and reliable product oversight".